Added Adler32 to System.IO.Hashing.

src/libraries/System.IO.Hashing/ref/System.IO.Hashing.cs

@@ -6,6 +6,23 @@
 
 namespace System.IO.Hashing
 {
+    public sealed partial class Adler32 : System.IO.Hashing.NonCryptographicHashAlgorithm
+    {
+        public Adler32() : base (default(int)) { }
+        public override void Append(System.ReadOnlySpan<byte> source) { }
+        public System.IO.Hashing.Adler32 Clone() { throw null; }
+        [System.CLSCompliantAttribute(false)]
+        public uint GetCurrentHashAsUInt32() { throw null; }
+        protected override void GetCurrentHashCore(System.Span<byte> destination) { }
+        protected override void GetHashAndResetCore(System.Span<byte> destination) { }
+        public static byte[] Hash(byte[] source) { throw null; }
+        public static byte[] Hash(System.ReadOnlySpan<byte> source) { throw null; }
+        public static int Hash(System.ReadOnlySpan<byte> source, System.Span<byte> destination) { throw null; }
+        [System.CLSCompliantAttribute(false)]
+        public static uint HashToUInt32(System.ReadOnlySpan<byte> source) { throw null; }
+        public override void Reset() { }
+        public static bool TryHash(System.ReadOnlySpan<byte> source, System.Span<byte> destination, out int bytesWritten) { throw null; }
+    }
     public sealed partial class Crc32 : System.IO.Hashing.NonCryptographicHashAlgorithm
     {
         public Crc32() : base (default(int)) { }

src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj

@@ -13,6 +13,7 @@ System.IO.Hashing.XxHash32</PackageDescription>
   </PropertyGroup>
 
   <ItemGroup>
+    <Compile Include="System\IO\Hashing\Adler32.cs" />
     <Compile Include="System\IO\Hashing\Crc32.cs" />
     <Compile Include="System\IO\Hashing\Crc32.Table.cs" />
     <Compile Include="System\IO\Hashing\Crc64.cs" />

src/libraries/System.IO.Hashing/src/System/IO/Hashing/Adler32.cs

@@ -0,0 +1,210 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Buffers.Binary;
+
+namespace System.IO.Hashing
+{
+    /// <summary>
+    ///   Provides an implementation of the Adler-32 algorithm, as used in
+    ///   RFC1950.
+    /// </summary>
+    /// <remarks>
+    ///   <para>
+    ///     The Adler-32 algorithm is designed for fast, lightweight integrity checking and is commonly used in
+    ///     data compression and transmission scenarios. This class is not suitable for cryptographic purposes.
+    ///   </para>
+    ///   <para>
+    ///     Adler-32 is not as robust as other checksum algorithms like CRC32, but it is faster to compute.
+    ///   </para>
+    /// </remarks>
+    public sealed partial class Adler32 : NonCryptographicHashAlgorithm
+    {
+        private const uint InitialState = 1u;
+        private const int Size = sizeof(uint);
+        private uint _adler = InitialState;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Adler32"/> class.
+        /// </summary>
+        public Adler32()
+            : base(Size)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Adler32"/> class using the state from another instance.
+        /// </summary>
+        private Adler32(uint adler)
+            : base(Size)
+            => _adler = adler;
+
+        /// <summary>
+        /// Returns a clone of the current instance, with a copy of the current instance's internal state.
+        /// </summary>
+        /// <returns>
+        /// A new instance that will produce the same sequence of values as the current instance.
+        /// </returns>
+        public Adler32 Clone()
+            => new(_adler);
+
+        /// <summary>
+        /// Appends the contents of <paramref name="source"/> to the data already
+        /// processed for the current hash computation.
+        /// </summary>
+        /// <param name="source">The data to process.</param>
+        public override void Append(ReadOnlySpan<byte> source)
+            => _adler = Update(_adler, source);
+
+        /// <summary>
+        /// Resets the hash computation to the initial state.
+        /// </summary>
+        public override void Reset()
+            => _adler = InitialState;
+
+        /// <summary>
+        /// Writes the computed hash value to <paramref name="destination"/>
+        /// without modifying accumulated state.
+        /// </summary>
+        /// <param name="destination">The buffer that receives the computed hash value.</param>
+        protected override void GetCurrentHashCore(Span<byte> destination)
+            => BinaryPrimitives.WriteUInt32BigEndian(destination, _adler);
+
+        /// <summary>
+        /// Writes the computed hash value to <paramref name="destination"/>
+        /// then clears the accumulated state.
+        /// </summary>
+        protected override void GetHashAndResetCore(Span<byte> destination)
+        {
+            BinaryPrimitives.WriteUInt32BigEndian(destination, _adler);
+            _adler = InitialState;
+        }
+
+        /// <summary>
+        /// Gets the current computed hash value without modifying accumulated state.
+        /// </summary>
+        /// <returns>
+        /// The hash value for the data already provided.
+        /// </returns>
+        [CLSCompliant(false)]
+        public uint GetCurrentHashAsUInt32()
+            => _adler;
+
+        /// <summary>
+        /// Computes the Adler-32 hash of the provided data.
+        /// </summary>
+        /// <param name="source">The data to hash.</param>
+        /// <returns>The Adler-32 hash of the provided data.</returns>
+        /// <exception cref="ArgumentNullException">
+        /// <paramref name="source"/> is <see langword="null"/>.
+        /// </exception>
+        public static byte[] Hash(byte[] source)
+        {
+            ArgumentNullException.ThrowIfNull(source);
+            return Hash(new ReadOnlySpan<byte>(source));
+        }
+
+        /// <summary>
+        /// Computes the Adler-32 hash of the provided data.
+        /// </summary>
+        /// <param name="source">The data to hash.</param>
+        /// <returns>The Adler-32 hash of the provided data.</returns>
+        public static byte[] Hash(ReadOnlySpan<byte> source)
+        {
+            byte[] ret = new byte[Size];
+            uint hash = HashToUInt32(source);
+            BinaryPrimitives.WriteUInt32BigEndian(ret, hash);
+            return ret;
+        }
+
+        /// <summary>
+        /// Attempts to compute the Adler-32 hash of the provided data into the provided destination.
+        /// </summary>
+        /// <param name="source">The data to hash.</param>
+        /// <param name="destination">The buffer that receives the computed hash value.</param>
+        /// <param name="bytesWritten">
+        /// On success, receives the number of bytes written to <paramref name="destination"/>.
+        /// </param>
+        /// <returns>
+        /// <see langword="true"/> if <paramref name="destination"/> is long enough to receive
+        /// the computed hash value (4 bytes); otherwise, <see langword="false"/>.
+        /// </returns>
+        public static bool TryHash(ReadOnlySpan<byte> source, Span<byte> destination, out int bytesWritten)
+        {
+            if (destination.Length < Size)
+            {
+                bytesWritten = 0;
+                return false;
+            }
+
+            uint hash = HashToUInt32(source);
+            BinaryPrimitives.WriteUInt32BigEndian(destination, hash);
+            bytesWritten = Size;
+            return true;
+        }
+
+        /// <summary>
+        /// Computes the Adler-32 hash of the provided data into the provided destination.
+        /// </summary>
+        /// <param name="source">The data to hash.</param>
+        /// <param name="destination">The buffer that receives the computed hash value.</param>
+        /// <returns>
+        /// The number of bytes written to <paramref name="destination"/>.
+        /// </returns>
+        public static int Hash(ReadOnlySpan<byte> source, Span<byte> destination)
+        {
+            if (destination.Length < Size)
+            {
+                ThrowDestinationTooShort();
+            }
+
+            uint hash = HashToUInt32(source);
+            BinaryPrimitives.WriteUInt32BigEndian(destination, hash);
+            return Size;
+        }
+
+        /// <summary>
+        /// Computes the Adler-32 hash of the provided data.
+        /// </summary>
+        /// <param name="source">The data to hash.</param>
+        /// <returns>
+        /// The computed Adler-32 hash.
+        /// </returns>
+        [CLSCompliant(false)]
+        public static uint HashToUInt32(ReadOnlySpan<byte> source)
+            => Update(InitialState, source);
+
+        private static uint Update(uint adler, ReadOnlySpan<byte> buf)
+        {
+            if (buf.IsEmpty)
+            {
+                return adler;
+            }
+
+            return UpdateScalar(adler, buf);
+        }
+
+        private static uint UpdateScalar(uint adler, ReadOnlySpan<byte> buf)
+        {
+            const uint Base = 65521; // largest prime smaller than 65536
+            const int NMax = 5552; // NMax is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1
+
+            uint s1 = adler & 0xFFFF;
+            uint s2 = (adler >> 16) & 0xFFFF;
+            while (buf.Length > 0)
+            {
+                int k = buf.Length < NMax ? buf.Length : NMax;
+                foreach (byte b in buf.Slice(0, k))
+                {
+                    s1 += b;
+                    s2 += s1;
+                }
+                s1 %= Base;
+                s2 %= Base;
+                buf = buf.Slice(k);
+            }
+
+            return (s2 << 16) | s1;
+        }
+    }
+}